1. Field of the Invention
The present invention relates to a mobile communication system based on the principles of CDMA (Code Division Multiplex Access), and more particularly to a receiving circuit in a mobile terminal in a mobile communication system based on the principles of CDMA.
2. Description of the Related Art
In recent years, mobile communication systems are finding a growing number of subscribers and are required to increase their capacity to accommodate subscribers. One approach to an increased capacity to accommodate subscribers is a technique known as CDMA in which one frequency band is shared by signals spread by a plurality of mathematically orthogonal codes.
In a CDMA mobile communication system, the receiving circuit of each mobile terminal has a plurality of finger receivers for inversely diffusing transmitted data in association with respective multiple paths. The transmitted data are inversely diffused by the finger receivers and then synthesized with each other.
FIG. 1 of the accompanying drawings shows in block form a finger receiver which is being experimentally studied by the inventors of the present application.
As shown in FIG. 1, the finger receiver comprises an inverse diffuser 1 for complex-inverse diffusing transmitted data at each chip rate for five points of xe2x88x921/2xcfx80, xe2x88x921/4xcfx80, 0xcfx80, +1/4xcfx80, +1/2xcfx80 at 16.384 MHz with respect to a reference point, a symbol accumulative adder 2 for accumulating and adding the data complex-inverse diffused by the inverse diffuser 1 in each symbol rate interval with respect to the above five points, a symbol power calculator 3 for converting the symbol data accumulated and added by the symbol accumulative adder 2 into power values and outputting the power values, a slot power accumulative adder 4 for accumulating and adding the power values for the five points outputted from the symbol power calculator 3 in a slot rate interval, a maximum value detector 5 for detecting one of the five complex-inverse diffusing points where the accumulated slot power value is maximum, based on the result produced by the slot power accumulative adder 4, and a symbol data selector 6 for outputting, to a circuit at a later stage (not shown), the accumulated and added data at the point where the power value is maximum, which has been detected by the maximum value detector 5, of those the symbol data accumulated and added by the symbol accumulative adder 2.
Operation of the finger receiver shown in FIG. 1 will be described below.
FIG. 2 of the accompanying drawings is a flowchart of the operation of the finger receiver shown in FIG. 1, and FIG. 3 of the accompanying drawings shows received data, illustrating how the finger receiver shown in FIG. 1 operates.
When data transmitted from a base station facility (not shown) is received in step S101, the inverse diffuser 1 inversely diffuses the transmitted data at a chip rate of 4.096 MHz using an inversely diffusing code in step S102. In step S102, the chip rate is divided into four timings, and the transmitted data is inversely diffused for five points of xe2x88x921/2xcfx80, xe2x88x921/4xcfx80, 0xcfx80, +1/4xcfx80, +1/2xcfx80 at 16.384 MHz.
Then, the symbol accumulative adder 2 accumulates and adds the data complex-inverse diffused by the inverse diffuser 1 in each symbol rate interval with respect to the above five points in step S103.
The symbol power calculator 3 converts the symbol data accumulated and added by the symbol accumulative adder 2 into power values and outputs the power values in step S104.
The slot power accumulative adder 4 accumulates and adds the power values at the five points outputted from the symbol power calculator 3 in one time slot rate interval in step S105.
Then, the maximum value detector 5 detects one of the five complex-inverse diffusing points where the accumulated slot power value is maximum, based on the result produced by the slot power accumulative adder 4 in step S106.
Thereafter, the point detected by the maximum value detector 5 is supplied to the symbol data selector 6. The symbol data selector 6 has been supplied with symbol data in a slot next to the slot where the accumulated slot power value is maximum as detected by the maximum value detector 5.
The symbol data selector 6 outputs, to a circuit at a later stage, the accumulated and added data at the point where the power value is maximum, which has been detected by the maximum value detector 5, i.e., the accumulated and added data at the point where the accumulated power is maximum as detected in the preceding slot, of those symbol data accumulated and added by the symbol accumulative adder 2 in step S107.
As described above, the chip rate is divided into a plurality of timings, and a received power is calculated at each of the timings. Data in a next slot at the timing where the received power is maximum is extracted and outputted to the circuit at the later stage for thereby increasing the quality of received data.
In a receiving circuit having finger receivers of the type described above, one of the five complex-inverse diffusing points where the accumulated slot power value is maximum is detected on the basis of the result produced by the slot power accumulative adder. If the transmitted data is burst data as in a paging channel (PCH), then the point where the accumulated slot power value is maximum is detected at a noise level for a slot free of received data, and data at the point detected as having the maximum value is extracted from the accumulated and added symbol data in a next slot and outputted to the circuit at the later stage. Therefore, an optimum complex-inverse diffusing point is not selected in the next slot, resulting in a degraded received-data quality.
It is therefore an object of the present invention to provide a receiving circuit which is capable of increasing the quality of received data even if transmitted data is burst data as in a paging channel.
To achieve the above object, there is provided in accordance with the present invention a receiving circuit comprising an antenna and a radio unit for receiving data, a plurality of finger receivers for inversely diffusing the data received by antenna and the radio unit in association with respective multiple paths, and a synthesizer for synthesizing datan inversely diffused by the finger receivers, each of the finger receivers comprising means for dividing a reception timing in each predetermined interval into a plurality of timings, inversely diffusing the received data at each of the timings, detecting one of the timings where a reception level is highest based on the inversely diffused data, and outputting data in a next interval at the detected timing.
Each of the finger receivers may comprise means for deciding whether there is received data or not based on the reception level at the timing where the reception level is highest, outputting the data in the next interval at the timing where the reception level is highest if it is determined that there is received data, and outputting the data in the next interval at the timing of presently outputting the data if it is determined that there is no received data.
Each of the finger receivers may comprise an inverse diffuser for dividing a chip rate into a plurality of reception timings and complex-inverse diffusing data received via the antenna and the radio unit at each of the reception timings, a symbol accumulative adder for accumulating and adding the data complex-inverse diffused by the inverse diffuser in each symbol rate interval at each of the reception timings, a symbol power calculator for converting symbol data accumulated and added by the symbol accumulative adder into power values and outputting the power values, a slot power accumulative adder for accumulating and adding the power values at the reception timings outputted from the symbol power calculator in a slot rate interval, a maximum value detector for detecting one of the reception timings where an accumulated slot power value is maximum based on a result produced by the slot power accumulative adder, a data decision unit for deciding whether there is received data or not based on the accumulated slot power value at the reception timing detected as having the maximum accumulated slot power value by the maximum value detector, and a symbol data selector for outputting accumulated and added symbol data at the reception timing detected as having the maximum accumulated slot power value by the maximum value detector, of those symbol data accumulated and added by the symbol accumulative adder if the data decision unit determines that there is received data, and outputting accumulated and added symbol data at the same reception timing as the accumulated and added symbol data outputted in a preceding slot, of those symbol data accumulated and added by the symbol accumulative adder if the data decision unit determines that there is no received data.
The data decision unit may comprise means for comparing the accumulated slot power value at the reception timing detected as having the maximum accumulated slot power value by the maximum value detector, with a predetermined threshold value thereby to decide whether there is received data or not.
Each of the finger receivers may have a switching unit for outputting the reception timing detected as having the maximum accumulated slot power value by the maximum value detector only if the data decision unit determines that there is received data, the symbol data selector comprising means for outputting accumulated and added symbol data at the reception timing detected as having the maximum accumulated slot power value by the maximum value detector, of those symbol data accumulated and added by the symbol accumulative adder if the symbol data selector is supplied with the reception timing detected as having the maximum accumulated slot power value by the maximum value detector via the switching unit, and outputting accumulated and added symbol data at the same reception timing as the accumulated and added symbol data outputted in the preceding slot, of those symbol data accumulated and added by the symbol accumulative adder if the symbol data selector is not supplied with the reception timing detected as having the maximum accumulated slot power value by the maximum value detector via the switching unit.
Alternatively, each of the finger receivers may comprise an inverse diffuser for dividing a chip rate into a plurality of reception timings and complex-inverse diffusing data received via the antenna and the radio unit at each of the reception timings, a symbol accumulative adder for accumulating and adding the data complex-inverse diffused by the inverse diffuser in each symbol rate interval at each of the reception timings, a symbol power calculator for converting symbol data accumulated and added by the symbol accumulative adder into power values and outputting the power values, a maximum value detector for detecting one of the reception timings where a symbol power value is maximum based on the power values at the reception timings outputted from the symbol power calculator, a data decision unit for deciding whether there is received data or not based on the symbol power value at the reception timing detected as having the maximum symbol power value by the maximum value detector, and a symbol data selector for outputting accumulated and added symbol data at the reception timing detected as having the maximum symbol power value by the maximum value detector, of those symbol data accumulated and added by the symbol accumulative adder if the data decision unit determines that there is received data, and outputting accumulated and added symbol data at the same reception timing as the accumulated and added symbol data outputted with a preceding symbol, of those symbol data accumulated and added by the symbol accumulative adder if the data decision unit determines that there is no received data.
The data decision unit may comprise means for comparing the symbol power value at the reception timing detected as having the maximum symbol power value by the maximum value detector, with a predetermined threshold value thereby to decide whether there is received data or not.
Each of the finger receivers may have a switching unit for outputting the reception timing detected as having the maximum symbol power value by the maximum value detector only if the data decision unit determines that there is received data, the symbol data selector comprising means for outputting accumulated and added symbol data at the reception timing detected as having the maximum symbol power value by the maximum value detector, of those symbol data accumulated and added by the symbol accumulative adder if the symbol data selector is supplied with the reception timing detected as having the maximum symbol power value by the maximum value detector via the switching unit, and outputting accumulated and added symbol data at the same reception timing as the accumulated and added symbol data outputted with the preceding symbol, of those symbol data accumulated and added by the symbol accumulative adder if the symbol data selector is not supplied with the reception timing detected as having the maximum symbol power value by the maximum value detector via the switching unit.
Alternatively, each of the finger receivers may comprise an inverse diffuser for dividing a chip rate into a plurality of reception timings and complex-inverse diffusing data received via the antenna and the radio unit at each of the reception timings, a symbol accumulative adder for accumulating and adding the data complex-inverse diffused by the inverse diffuser in each symbol rate interval at each of the reception timings, a symbol S/N ratio calculator for calculating S/N ratios of received data from symbol data accumulated and added by the symbol accumulative adder and outputting the calculated S/N ratios, a slot S/N ratio accumulative adder for accumulating and adding the S/N ratios at the reception timings outputted from the symbol S/N ratio calculator, a maximum value detector for detecting one of the reception timings where an accumulated slot S/N ratio is maximum based on a result produced by the slot S/N ratio accumulative adder, a data decision unit for deciding whether there is received data or not based on the accumulated slot S/N ratio at the reception timing detected as having the maximum accumulated slot S/N ratio by the maximum value detector, and a symbol data selector for outputting accumulated and added symbol data at the reception timing detected as having the maximum accumulated slot S/N ratio by the maximum value detector, of those symbol data accumulated and added by the symbol accumulative adder if the data decision unit determines that there is received data, and outputting accumulated and added symbol data at the same reception timing as the accumulated and added symbol data outputted in a preceding slot, of those symbol data accumulated and added by the symbol accumulative adder if the data decision unit determines that there is no received data.
The data decision unit may comprise means for comparing the accumulated slot S/N ratio at the reception timing detected as having the maximum accumulated slot S/N ratio by the maximum value detector, with a predetermined threshold value thereby to decide whether there is received data or not.
Each of the finger receivers may have a switching unit for outputting the reception timing detected as having the maximum accumulated slot S/N ratio by the maximum value detector only if the data decision unit determines that there is received data, the symbol data selector comprising means for outputting accumulated and added symbol data at the reception timing detected as having the maximum accumulated slot S/N ratio by the maximum value detector, of those symbol data accumulated and added by the symbol accumulative adder if the symbol data selector is supplied with the reception timing detected as having the maximum accumulated slot S/N ratio by the maximum value detector via the switching unit, and outputting accumulated and added symbol data at the same reception timing as the accumulated and added symbol data outputted in the preceding slot, of those symbol data accumulated and added by the symbol accumulative adder if the symbol data selector is not supplied with the reception timing detected as having the maximum accumulated slot S/N ratio by the maximum value detector via the switching unit.
Further alternatively, each of the finger receivers may comprise an inverse diffuser for dividing a chip rate into a plurality of reception timings and complex-inverse diffusing data received via the antenna and the radio unit at each of the reception timings, a symbol accumulative adder for accumulating and adding the data complex-inverse diffused by the inverse diffuser in each symbol rate interval at each of the reception timings, a symbol S/N ratio calculator for calculating S/N ratios of received data from symbol data accumulated and added by the symbol accumulative adder and outputting the calculated S/N ratios, a maximum value detector for detecting one of the reception timings where a symbol S/N ratio is maximum based on the S/N ratios at the reception timings outputted from the symbol S/N ratio calculator, a data decision unit for deciding whether there is received data or not based on the symbol S/N ratio at the reception timing detected as having the maximum symbol S/N ratio by the maximum value detector, and a symbol data selector for outputting accumulated and added symbol data at the reception timing detected as having the maximum symbol S/N ratio by the maximum value detector, of those symbol data accumulated and added by the symbol accumulative adder if the data decision unit determines that there is received data, and outputting accumulated and added symbol data at the same reception timing as the accumulated and added symbol data outputted with a preceding symbol, of those symbol data accumulated and added by the symbol accumulative adder if the data decision unit determines that there is no received data.
The data decision unit may comprise means for comparing the symbol S/N ratio at the reception timing detected as having the maximum symbol S/N ratio by the maximum value detector, with a predetermined threshold value thereby to decide whether there is received data or not.
Each of the finger receivers may have a switching unit for outputting the reception timing detected as having the maximum symbol S/N ratio by the maximum value detector only if the data decision unit determines that there is received data, the symbol data selector comprising means for outputting accumulated and added symbol data at the reception timing detected as having the maximum symbol S/N ratio by the maximum value detector, of those symbol data accumulated and added by the symbol accumulative adder if the symbol data selector is supplied with the reception timing detected as having the maximum symbol S/N ratio by the maximum value detector via the switching unit, and outputting accumulated and added symbol data at the same reception timing as the accumulated and added symbol data outputted with the preceding symbol, of those symbol data accumulated and added by the symbol accumulative adder if the symbol data selector is not supplied with the reception timing detected as having the maximum symbol S/N ratio by the maximum value detector via the switching unit.
According to the present invention, there is also provided a mobile terminal in a mobile communication system, the mobile terminal having the receiving circuit described above.
According to the present invention, there is further provided a method of receiving data transmitted by way of mobile communications, comprising the steps of dividing a reception timing in each predetermined interval into a plurality of timings and inversely diffusing the received data at each of the timings, detecting one of the timings where a reception level is highest based on the inversely diffused data, and outputting data in a next interval at the detected timing.
The method may further comprise the steps of deciding whether there is received data or not based on the reception level at the timing where the reception level is highest, outputting the data in the next interval at the timing where the reception level is highest if it is determined that there is received data, and outputting the data in the next interval at the timing of presently outputting the data if it is determined that there is no received data.
With the arrangement of the present invention, as described above, in the finger receivers, the reception timing in each predetermined interval is divided into a plurality of timings, and the received data is inversely diffused at each of the timings. Based on the inversely diffused data, the timing where the reception level is the highest is detected, and data in a next interval is outputted at the detected timing. Therefore, the quality of received data can be increased.
Whether there is received data or not is decided based on the reception level at the timing where the reception level is the highest. If it is determined that there is received data, then data in a next interval is outputted at the timing where the reception level is the highest. If it is determined that there is no received data, then data in a next interval is outputted at the timing of presently outputting data. In such an arrangement, if the received data is burst data as in a paging channel, then since the detection of timing in the data is not reflected in the outputting of the data, the quality of received data can be increased even though the received data is burst data as in a paging channel.
The above and other objects, features, and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate examples of the present invention.